In short: Pentair replacement O-ring for pump prefilter cover, size #2-357. Pentair part number 357255Z.
Air in the pump basket?
The prefilter cover is the point in the circuit where the pressure is lowest. It is therefore the only place where air can enter instead of water exiting, making the leak invisible.
The result is visible in the basket: a growing air bubble, a drop in flow, and a pump that loses prime after stopping. If prolonged, this cavitation damages the mechanical seal and the impeller.
The cover O-ring is a wear part. It is replaced, not repaired.
Official Pentair specifications
| Part number |
357255Z |
| Size |
#2-357 |
| Type |
Prefilter cover O-ring |
| Original part |
Yes, Pentair part |
Frequently asked questions
How to locate the air leak?
With the pump running, pour water around the cover. If the bubble decreases, air was indeed entering there. Also check the drain plug and the suction-side fittings.
Should it be greased?
Yes, a thin layer of pool silicone grease. Never use Vaseline.
When to replace it?
Inspect it every time you open the pool. A flattened, hardened, or cracked O-ring must be replaced. It is an inexpensive part that prevents costly problems.
Service on the North Shore
Piscines Geyser keeps Pentair parts in stock in Blainville and serves the Laurentians. Send us a photo of your installation if you are unsure about compatibility: we will confirm before shipping.
